1. Field of the Invention
This invention relates to diamond insert drag bits and a method to interference fit the inserts within the face of the bit.
More particularly, this invention relates to diamond insert drag bits wherein the insert boring operation results in additional support for the shank of the insert interference fitted within the face of the bit.
2. Description of the Prior Art
State of the art methods to insert diamond insert studs within the face of a drag bit body result in a concentric counterbored hole to relieve an area surrounding the insert body to clear the bottom edge of the cutting face of the diamond insert.
Each of the multiplicity of diamond inserts utilized in a typical drag bit is so oriented in the face portion of the drag bit to maximize borehole penetration. In other words, the cutting face of each insert is positioned to cut a specific area on the borehole bottom to maximize hole penetration.
Experience has shown that some of the strategically positioned diamond insert studs supporting the diamond cutting face of the inserts have a tendency to fracture just above the grip length of the studs during operation of the bit.
Heretofore there has been no means provided to backup the upper portion of the insert stud body above the grip length of the insert.
Therefore, state of the art diamond insert drag bits are disadvantaged in that each of the multiplicity of inserts is vulnerable to breakage just above the top of the grip length of the insert studs.
The present invention overcomes this disadvantage by counterboring each insert hole in an eccentric manner. The eccentric counterbore hole, for example, substantially tangents the insert hole at a point 180.degree. from the orientation of the cutting tip of each of the inserts, thus providing backup support for the portion of the shank of the insert that normally is unsupported in conventional concentric counterboring operations.